Step 1: Preheat the Waffle Maker. Start by preheating your waffle maker according to the manufacturer's instructions.
Step 2: Combine Dry Ingredients. In a large mixing bowl, whisk together the flour, cornstarch, baking powder, baking soda, and salt until well combined.
Step 3: Mix Wet Ingredients. In another bowl, whisk together the buttermilk, milk, vegetable oil, vanilla extract, and egg yolks until smooth.
Step 4: Beat Egg Whites. In a clean mixing bowl, beat the egg whites until soft peaks form. Gradually add the sugar and continue beating until stiff peaks form.
Step 5: Combine Mixtures. Pour the wet ingredients into the dry ingredients and stir until just combined. Gently fold in the beaten egg whites.
Step 6: Cook the Waffles. Pour the batter into the preheated waffle maker and cook according to your waffle maker's instructions.
Step 7: Serve and Enjoy. Carefully remove the waffles and serve immediately with your favorite toppings.